Ratcheted spinal device

ABSTRACT

A ratcheted spinal device including a variable-length member including a ratchet mechanism that has an operative configuration that allows a change in length of the variable-length member in one direction and prevents a change in length of the variable-length member in an opposite direction, wherein the variable-length member includes polyaxial-joint attachment members for attachment to bone, which permit pivoting movement of the attachment members about more than one pivoting axis.

FIELD OF THE INVENTION

The present invention relates generally to spinal implants andprostheses, and particularly to a spinal rod having a ratchet mechanism,and also having a locked position and a released position.

BACKGROUND OF THE INVENTION

Scoliosis is a spinal deformity affecting many people. Current surgicaltreatment involves affixing long fusion rods to the spine by pediclescrews. The rod system is intended to force the deformed spine into amore healthy position.

Unfortunately, there are severe shortcomings to this procedure; thedeformation is rarely perfectly corrected, the long fusion for life isnot a desired clinical situation and failures are not uncommon.

SUMMARY OF THE INVENTION

The present invention seeks to provide an improved ratcheted spinaldevice that can be lengthened or shortened using a ratchet mechanism.The device has a variable-length member that can be connected tostandard pedicle screws as well as to other spinal rods, usingappropriate connectors. The variable-length member can also be directlyconnected to, or be supported by, bony elements of the spine.

In one embodiment of the invention, the device can be set to threedifferent configurations:

a. Ratchet mechanism active and the variable-length member can change inlength (extend or contract) in one direction.

b. Ratchet mechanism not active and the variable-length member can movein opposite directions corresponding to the extending and contractingdirections.

c. Locked position, wherein the length of the variable-length member isfixed.

In an embodiment of the invention, the selection of these configurationscan be done by rotating an internal element of the assembly. Forexample, the rotation of the internal element can be done using a wormgear mechanism. The worm gear can be activated by a shaft, through apercutaneous procedure or by an implantable mechanism such as anelectric motor, magnet arrangement or other means known to those skilledin the art.

In another embodiment of the present invention, the variable-lengthmember can have two portions with different rigidity. For example, thevariable-length member can have a flexible portion (e.g., when theratchet is built such that the rod can be only shortened) like aflexible cable, a rope, a flexible mechanical joint and other meansknown to those skilled in the art.

In another embodiment of the invention, useful when the rod is supporteddirectly by bone structure of the spine, the hook holding against thebone can have a second hook to fix it to the optimal position.

There is thus provided in accordance with an embodiment of the presentinvention a ratcheted spinal device including a variable-length memberincluding a ratchet mechanism that has an operative configuration thatallows a change in length of the variable-length member in one directionand prevents a change in length of the variable-length member in anopposite direction, wherein the variable-length member includespolyaxial-joint attachment members for attachment to bone, which permitpivoting movement of the attachment members about more than one pivotingaxis.

In accordance with an embodiment of the present invention the ratchetmechanism has another operative configuration in which thevariable-length member is locked in place, and yet another operativeconfiguration in which the ratchet mechanism is neutralized so that thevariable-length member is free to change in length in any of thedirections, and a controller controls selection of one of the operativeconfigurations.

In accordance with an embodiment of the present invention the controllerselectively moves a pawl of the ratchet mechanism into or out ofoperative alignment with teeth of the ratchet mechanism, and selectivelymoves a locking element into and out of locking engagement with thevariable-length member. The pawl and locking element may be mounted on aspindle rotated by the controller. Alternatively, the pawl and lockingelement may be mounted on an eccentric mechanism rotated by thecontroller.

In accordance with an embodiment of the present invention thepolyaxial-joint attachment members are located at or near opposite endsof the variable-length member.

In accordance with an embodiment of the present invention a biasingdevice is operative to apply an urging force on the variable-lengthmember.

In accordance with an embodiment of the present invention at least oneof the polyaxial-joint attachment members includes a ball-and-socketjoint. Additionally or alternatively, at least one of thepolyaxial-joint attachment members includes a hook.

In accordance with another embodiment of the present invention theratchet mechanism is toothless.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description, taken in conjunction with thedrawings in which:

FIG. 1 is a simplified illustration of a longitudinal cross section ofthe spinal device, constructed and operative in accordance with anembodiment of the invention;

FIG. 2 is a simplified illustration of a cross section perpendicular tothat of FIG. 1;

FIG. 3 is another simplified illustration of a longitudinal crosssection of the spinal device, including a biasing device, constructedand operative in accordance with another embodiment of the invention;

FIGS. 4A, 4B and 4C are simplified illustrations of three controlledpositions of the ratchet mechanism of FIG. 1;

FIG. 5 is a simplified pictorial illustration of a spinal device,constructed and operative in accordance with another embodiment of theinvention, designed to be shortened only, having a flexible portion;

FIGS. 6A and 6B are simplified pictorial illustrations of additionalmeans that can be used together with the device for optimal deformitycorrection, in accordance with an embodiment of the invention;

FIGS. 7, 8, 9A and 9B are simplified pictorial illustrations of spinalrod support elements placed directly against bony elements of the spine,in accordance with an embodiment of the invention;

FIG. 10 is a simplified illustration of a spinal device, constructed andoperative in accordance with another embodiment of the invention,connected to two bone screws;

FIG. 11 is a simplified pictorial cross section of the spinal device ofFIG. 10;

FIG. 12 is a simplified enlarged illustration of the control mechanismof the spinal device of FIG. 10;

FIG. 13 is a simplified pictorial illustration of an eye joint toconnect the device of FIG. 10 to a bone screw;

FIGS. 14 and 15 are simplified illustrations of toothless ratchetmechanisms for spinal devices, in accordance with embodiments of theinvention.

DETAILED DESCRIPTION OF EMBODIMENTS

Reference is now made to FIG. 1, which illustrates a ratcheted spinaldevice 10, constructed and operative in accordance with a non-limitingembodiment of the invention.

The ratcheted spinal device 10 includes a variable-length member 12. Inthe illustrated embodiment, the variable-length member 12 is a rod. Theterm “rod” encompasses any slender element of any size andcross-sectional shape, such as but not limited to, a rod, bar, wire andthe like.

The ratcheted spinal device 10 includes a ratchet mechanism 14, whichhas an operative configuration that allows a change in length of thevariable-length member 12 in one direction and prevents a change inlength of the variable-length member 12 in an opposite direction, aswill be explained further below.

In the illustrated embodiment of FIG. 1, ratcheted spinal device 10includes a ratchet mechanism 14 that has ratchet teeth 16 formed alongan axial portion of variable-length member 12, and a pawl 18 arranged tocatch on one of the teeth 16. Pawl 18 is mounted on a drum 20 attachedto a spindle 22, which is rotated by a controller, which may be a wormgear drive 24 that meshes with gear teeth 26 formed at the end ofspindle 22.

One end 23 of variable-length member 12 is arranged to linearly movethrough an aperture 28 formed in a housing 30. Variable-length member 12includes two polyaxial-joint attachment members 32. In the illustratedembodiment, one polyaxial-joint attachment member 32 is positioned at ornear end 23 of variable-length member 12 and another polyaxial-jointattachment member 32 is positioned on housing 30. Alternatively, thevariable-length member 12 could be constructed so that the secondpolyaxial-joint attachment member 32 is mounted on it, at or near an endopposite to end 23. Both polyaxial-joint attachment members 32 are usedto attach device 10 to available bone structure of the spine (such as bymeans of pedicle screws that pass through members 32, as seen in FIG.10). The polyaxial-joint attachment members 32 permit pivoting movementabout more than one pivoting axis, such as about axis 33 (which isperpendicular to the drawing sheet of FIG. 1) and axes 34 and/or 35. Inthe embodiment of FIG. 1, one or both of polyaxial-joint attachmentmembers 32 have ball-and-socket joints. Additionally or alternatively,as shown in FIG. 3, one or both of polyaxial-joint attachment members 32include a hook 36.

After installation of device 10 in a patient, in a typical treatmentplan, the patient will be asked to bend in a direction that will causethe end 23 of variable-length member 12 to move further out of housing30 until ratchet teeth 16 click one increment (or more than oneincrement, if directed by the physician) past pawl 18. This extends thelength of variable-length member 12. Pawl 18 holds the variable-lengthmember 12 in place after the incremental length change. In this manner,the variable-length member 12 can be lengthened gradually with outcausing trauma to the patient.

Alternatively, the ratchet mechanism 14 can be set to allow ratchetedmovement of end 23 of variable-length member 12 into housing 30, therebyto shorten the length of variable-length member 12 for each incrementalbending of the patient, if the particular treatment plan calls forshortening the length.

In accordance with an embodiment of the present invention the ratchetmechanism 14 has another operative configuration in which thevariable-length member 12 is locked in place. This may be accomplishedby means of a locking element 38, which may be positioned on drum 20, asseen in FIG. 2, such as 90° away from pawl 18. The controller (worm geardrive 24) can rotate drum 20/spindle 22 so that pawl 18 is moved awayfrom and out of engagement with ratchet teeth 16, while at the same timelocking element 38 (which may be shaped similarly to pawl 18) is movedinto locking engagement with one or more of ratchet teeth 16 (seen inFIG. 4B).

In accordance with an embodiment of the present invention the ratchetmechanism 14 has yet another operative configuration in which theratchet mechanism 14 is neutralized so that variable-length member 12 isfree to change in length in any of the directions. This may beaccomplished by controller (worm gear drive 24) rotating spindle 22 soboth pawl 18 and locking element are moved away from and out ofengagement with ratchet teeth 16 (seen in FIG. 4C). The worm gear drive24 can be activated by a shaft 40, through a percutaneous procedure orby an implantable mechanism such as an electric motor, magnetarrangement or other means known to those skilled in the art.

Reference is now made to FIG. 3. In accordance with an embodiment of thepresent invention a biasing device 42 is operative to apply an urgingforce on the variable-length member 12. Biasing device 42 can be a metalspring, plastic spring, an elastomer or gas-actuated extensible rod orshock absorber. The biasing device 42 urges variable-length member 12 tofollow the motion direction dictated by ratchet mechanism 14.

Reference is now made to FIG. 5. In this embodiment, the variable-lengthmember 12 includes a rigid portion 44 and a flexible portion 46.Flexible portion 46 may be a cable, rope, plastic wire, flexiblemechanical joint or any other means that transfers a pulling force butdoes not transfer moments from attachment member 32 to rigid portion 44.

Reference is now made to FIGS. 6A and 6B, which illustrate devices thatcan be used in conjunction with the device 10 to optimally correctspinal deformity. In FIG. 6A, a flexure-limiting element 48 is deployedaround two or more vertebrae 49 to limit the amount of bending orflexion the patient can bend at this portion of the spine.Flexure-limiting element 48 can be a flexible band, wire, string or anyother means that prevents the spinous process from flexing too much.

In FIG. 6B, one or more flexure-limiting elements 50 are positionedbetween two or more vertebrae 48 to limit the amount of bending orflexion the patient can bend at this portion of the spine.Flexure-limiting elements 50 (which may also be used in FIG. 6A) can bemade of metal, plastic or any other rigid or semi-rigid material and canhave a rectangle, rounded, or elliptical cross section, or any othercross section that fits the anatomy.

Reference is now made to FIGS. 7 and 9A, which illustrate somesupporting elements for supporting or holding the device 10 directlyagainst bony elements of the spine. The supporting elements may beadditional, or instead of, the simple hooks illustrated in FIG. 3. Thenumeral 700 is a top sectional view of the spinal vertebra. A supportingelement 52 is firmly connected to the device 10 (not shown here).Supporting element 52 can be located above or under the transverseprocess. Usually one end of the rod will have a supporting elementlocated above one transverse process and the second end will have asupporting element located under a second transverse process. A hook 54holds the lamina of the same vertebra and a connecting element 56 fixessupporting element 52 to hook 54. This arrangement enables supportingelement 52 to be secured as close as possible to the origin of thetransverse process, its strongest point.

Reference is now made to FIGS. 8 and 9B, which illustrate anothersupporting means when the spinal rod is holding directly against thebony elements of the spine. The numeral 800 is a top sectional view ofthe spinal vertebra. A supporting element 58 is firmly connected to thedevice 10 (not shown here). Supporting element 58 can be located aboveor under the transverse process. Usually one end of the rod will have asupporting element located above one transverse process and the secondend will have a supporting element located under a second transverseprocess. A supporting element 60 is located on the opposite side of thespinous process of the same vertebra and a connecting element 62 fixessupporting element 58 to supporting element 60. This arrangement alsoenables supporting element 58 to be secured as close as possible to theorigin of the transverse process, its strongest point.

Reference is now made to FIGS. 10-13, which illustrates a ratchetedspinal device 100, constructed and operative in accordance with anothernon-limiting embodiment of the invention.

Similar to the embodiment of FIG. 1, ratcheted spinal device 100includes a ratchet mechanism 114, which has an operative configurationthat allows a change in length of a variable-length member 112 in onedirection and prevents a change in length of the variable-length member112 in an opposite direction. Ratchet mechanism 114 has ratchet teeth116 formed along an axial portion of variable-length member 112, and apawl 118 arranged to catch on one of the teeth 116. Pawl 118 extendsfrom a controller element 120 mounted about a pivot 122 and providedwith an eccentric cam 124. Rotation of eccentric cam 124 moves pawl 118to one of three positions: a) in ratchet engagement with teeth 116 sothat variable-length member 112 can incrementally move in one direction,b) in locked engagement with teeth 116 so that variable-length member112 cannot move at all, and c) moved out of engagement with teeth 116 sothat variable-length member 112 can move in both directions freely.

One end 123 of variable-length member 112 is arranged to linearly movethrough an aperture 128 formed in a housing 130. Variable-length member112 includes two polyaxial-joint attachment members 132. As similarlydescribed above, both polyaxial-joint attachment members 132 are used toattach device 100 to available bone structure of the spine, such as bymeans of pedicle screws 133 that pass through members 132, as seen inFIG. 10. FIG. 13 illustrates a head 135 of pedicle screw 133 passedthrough polyaxial-joint attachment member 132 (e.g., an eye joint),wherein a nut 134 firmly holds pedicle screw 133 in place while enablingpolyaxial rotation.

In the above embodiments, the ratchet mechanism has ratchet teeth. Inaccordance with another embodiment of the present invention the ratchetmechanism is toothless (continuous “ratchet”), which provides infinitepositions as opposed to discrete, incremental steps. Two examples areshown in FIGS. 14 and 15. In FIG. 14, a rod 140 is arranged for linearmotion in the direction of arrow 141. A disc 142 is eccentricallymounted about a pivot 144. The disc 142 contacts rod 140 at a point 146above a line 148, which is perpendicular to rod 140 and passes throughthe center of pivot 144. Rod 140 cannot move downwards (opposite toarrow 141), because it is wedged against disc 142 at point 146.

In FIG. 15, a wedge 150 contacts rod 140. Rod 140 cannot move downwards(opposite to arrow 141), because it is wedged against wedge 150.

Other toothless ratchet mechanism can be use, such as but not limitedto, the toothless ratchet and clutch mechanism in U.S. Pat. No.5,152,197.

It will be appreciated by persons skilled in the art that the presentinvention is not limited by what has been particularly shown anddescribed hereinabove. Rather the scope of the present inventionincludes both combinations and subcombinations of the features describedhereinabove as well as modifications and variations thereof which wouldoccur to a person of skill in the art upon reading the foregoingdescription and which are not in the prior art.

What is claimed is:
 1. A method for adjusting curvature of a spine comprising: installing a ratcheted spinal device into a patient, said ratcheted spinal device comprising a length member disposed in a housing, wherein each of said housing and said length member comprises a polyaxial-joint attachment member for attachment to bone, each of said polyaxial-joint attachment members permitting pivoting movement about more than one pivoting axis, and comprising pedicle screws that pass through said polyaxial-joint attachment members, and wherein for each of said pedicle screws a nut firmly holds said pedicle screw in place while still enabling polyaxial rotation of said pedicle screw even after the nut has been fully tightened; wherein installing the ratcheted spinal device into the patient comprises affixing said pedicle screws to a portion of a bone of a spine the patient, and for each of said pedicle screws, tightening said nut to firmly hold said pedicle screw in place while still enabling polyaxial rotation of said pedicle screw even after the nut has been fully tightened; and wherein movement of an end of said length member that protrudes out of said housing, either further out of or further into said housing, adjusts curvature of the spine.
 2. A method for adjusting curvature of a spine comprising: installing a ratcheted spinal device into a patient, said ratcheted spinal device comprising a length member disposed in a housing, said length member comprising all portions having a length that protrudes out of said housing a variable amount, said length member and said housing comprising a ratchet mechanism that has an operative configuration that allows a change in the length that said length member protrudes out of said housing in one direction, wherein each of said housing and said length member comprises a polyaxial-joint attachment member for attachment to bone, each of said polyaxial-joint attachment members permitting pivoting movement about more than one pivoting axis, and comprising pedicle screws that pass through said polyaxial-joint attachment members, and wherein for each of said pedicle screws a nut firmly holds said pedicle screw in place while still enabling polyaxial rotation of said pedicle screw even after the nut has been fully tightened; wherein said ratchet mechanism comprises ratchet teeth formed along an axial portion of said length member and a pawl arranged to catch on one of the ratchet teeth; wherein installing the ratcheted spinal device into the patient comprises affixing said pedicle screws to a portion of a bone of a spine the patient, and for each of said pedicle screws, tightening said nut to firmly hold said pedicle screw in place while still enabling polyaxial rotation of said pedicle screw even after the nut has been fully tightened; and wherein movement of an end of said length member that protrudes out of said housing, either further out of or further into said housing until ratchet teeth of said ratcheted spinal device click at least one increment past said pawl, adjusts curvature of the spine. 